Sonic 3 Complete | Customizer

Randomizer mode – shuffle monitors, badniks, ring placements
Online sharing hub – upload custom profiles with ratings
Integrated launcher – launch directly into an emulator (e.g., BlastEm, BizHawk)

Fire up your emulator, open the Customizer, and build the Sonic 3 that Sega should have let you play in 1994.

Load ROM

The "Lock-On" Logic: You can finally play as Knuckles in Sonic 3 levels with his unique routes and climbing sections, or play through Sonic 3 & Knuckles as a continuous, singular adventure without the "save screen" break between Launch Base and Mushroom Hill.
Gameplay Tweaks: Want the spindash to behave like Sonic 2? Or prefer the difficulty of the original release? You can toggle specific mechanics, fix the "gliding glitch," or even enable the elemental shields to display on the HUD.
The "OG" Soundtrack: For those who prefer the original Michael Jackson-influenced tracks (like the Carnival Night and Ice Cap Zone themes) over the PC Collection replacements, the customizer lets you swap the music back. It’s a massive win for preservationists.
Cosmetic Overhaul: You can change the color of the HUD, swap Sonic’s sprites to resemble the CD/2 style, or even change the appearance of the shields.

S3C ROM hack uses a settings block appended to the end of the ROM or stored in a separate .s3c config file.
The Customizer reads/writes a 512‑byte (or larger) configuration header located at a fixed offset.
Workflow: